Well, didn't she spoil to Kurokawa that she was the one showing Nanaki the picture of her cheating boyfriend? I mean, obvs. it's the right thing to do as a friend. But did she really had to show this to her when they were surrounded by so many people? This doesn't seem sensible to me. Also she probably realised that superficial-af-Nanaki didn't really like him for him, but for status. This time ought to be different.
It looks like I'm basically the only one who still likes Izumi at this point. She's manipulative oc, but what you gonna do if you're smarter than anyone else in the group trying to push things towards your advantage? The moral will obvs. be that you shouldn't do that, but I still like her character-design.

Ok I can't really hate Izumi after the last Chapter. It's clearly indicated that she had feelings for Nanaki since forever.
It's gotta hurt to see her taken away, first by some a**hole guy, next time by another girl (even if they don't realise their feelings). Sure, she does it the wrong way. For example she showed Nanaki the picture of her cheating (ex)boyfriend in front of all the other girls. This had to be calculated, it just backfired. She's a teenage girl that has to handle her feelings for someone she thought she'd never have a chance with, but suddenly she develops feelings for a girl? Damn, poor Izumi.
(Not gonna lie, tho. If all of the signals are just misleading af and she actually likes Kanade, I'll be surprised)

Izumi's development in this Chapter is the first thing not awfully chliché about this story (Don't get me wrong, I enjoy it, but still). Izumi showed to be a pretty decent character until now and she's hands down my favourite. To see she's not only a Mary Sue-ish character makes it only better. I doubt she'll throughly manipulate Nanaki, though. She'll probably see at some point she's hurting her, confess and make Nanaki realise her feelings for Kurokawa or something.